Addressing Wall Thickness Issues in Injection Molded Parts

When it comes to injection molding, the wall thickness is a key factor in determining the performance functionality, manufacturability, and functionality of the finished item. When clients present designs that have an unbalanced wall thicknesses that can lead to an array of issues with injection molding that could affect the integrity of the product and efficiency. Let’s look into this issue and find effective strategies to boost wall thickness, while keeping strength and structural strength.

The most significant concern of walls that are too thick is the greater chance of a variety of imperfections, including the warping of sinks, corrosion as well as internal gaps. This is due to inconsistencies in cooling between the outside and the inner piece. The walls that are thicker retain more heat and can cause the possibility of weak points in the structure. Additionally, parts with thick walls require longer cooling times. This will significantly affect the production process as well as boost the time to cycle.

To overcome these issues We suggest a dual-pronged strategy: decreasing the thickness of walls and adding reinforcing the ribs.

Reduce Wall Thickness by Making the wall thicker is a delicate compromise between the ability to manufacture and component quality. We recommend gradually decreasing the wall thickness until it is at an acceptable level that typically ranges between 2 and 4 millimeters for the majority of applications. It can add several benefits:

• A) Increased efficiency of cooling The thinner walls enable rapid and uniform cooling. This reduces the chance of sink marks and warpage.
• A) Cost savings: Less material is needed, leading to a lower cost and greener product.
• C) Reduced cycle time: A faster cooling process outcome in shorter cycle times and thus increasing the efficiency of production.
• D) Improved flow characteristics Thicker walls may rise the flow of material during injection which could result in a reduction in pressures.

Integrating Reinforcing Ribs into the Design: To make up for any weakening caused by a lower wall thickness We recommend strategically adding reinforced ribs within the plan. Ribs have several benefits:

• A) Support for structural design: Strongly designed ribs are a great way to increase the rigidity of the component and its load-bearing capacity.
• B) Reduced warpage Ribs benefit to distribute the stress uniformly across the whole which reduces the risk of warpage.
• C) Ribs can be used to rise strength without the need to go back to thick walls. This allows for the preservation of material costs.
• D) Design flexible: Rib patterns could be adapted to meet particular stress points or load bearing demands.

In designing your ribs, take into consideration these guidelines:

• Rib thickness is usually 50% to 60% of the adjacent wall’s thickness in order to avoid the sink marks.
• Keep an angle between 0.5 or 1° on the rib wall for ease of expulsion.
• Ring the base of the ribs to lessen stress.
• Beware of sharp corners, and use angles to improve flow and lessen the stress.

It’s crucial to keep in mind that the actual execution of these suggestions depends on the parts geometry, materials properties and the functional requirements. It is suggested to use computer-aided engineering (CAE) tools for example, like mold flow analysis to enhance the design repeatedly. This method allows simulation of various dimensions of walls and ribs prior to committing to physical models.

Also, think about the choice of the material attentively. Certain high-performance polymers can permit thinner walls and still retain the necessary mechanical properties. Collaboration with suppliers of materials could offer information on the latest developments in polymer technology which may benefit your particular application.

By decreasing the thickness of walls and by incorporating reinforced ribs into the design to address problems with injection molding that arise from a wall that is too thick. This method does not just solve manufacturing problems, but can also provide the potential for benefits such as reduction in material costs, cycle times reduced, as well as overall quality. It is important to remember that a successful implementation needs an understanding of component’s design, its material properties, as well as the manufacturing procedure. Through the process of iterative design and test we will be able to fulfil the best combination of manufacturability and quality.

How to solve the sink marks

The problem of sink marks of plastic injection parts (surface shrinkage and internal shrinkage) is due to the insufficient melt replenishment when the thick part is cooled.

We often encounter these sink mark problems. No matter how to increase the pressure, increase the water line numbers, and extend the injection time, the shrinkage problem is unsolvable.

Among the plastic raw materials, due to the rapid cooling rate, the abnormal sink problem of the PC injection molding is the most difficult to solve, and the abnormal sink problem of  PP material is also difficult to handle.

Therefore, it is necessary to take some unconventional injection molding techniques when encountering thick and large plastic part injection problems. Otherwise, it won’t be easy to deal with.

Here are some effective techniques to deal with the problems of this injection molding.

Ensuring that the injection molded parts are not deformed, the cooling time should be minimized as far as possible. The injection molded parts are prematurely ejected at a higher temperature.

At this time, the temperature of the outer layer of the injection molded part is still high, and the skin is not too hardened.

The temperature difference between the inside and the outside of the melt is relatively small, which is advantageous for the overall shrinkage, reducing the concentrated shrinkage inside the injection molded part.

Since the shrinkage amount of the injection molded part is constant, the more the overall shrinkage is, the smaller the concentrated shrinkage amount is. The degree of internal shrinkage and surface shrinkage is thus reduced.

the problem of sink and concavation is caused by the fact that the increased temperature of the mold surface will make cooling NOT enough.

The surface of the newly-formed injection molded part is still soft (unlike the PC part, the surface is hard and easy to invite shrinkage voids). The internal shrinkage, which is not eliminated, creates a vacuum.

It causes the surface of the injection molded part to compress inward under the pressure of atmospheric pressure, and at the same time, due to the contraction force, the problem of sink occurs.

Moreover, the slower the surface hardening speed is, the more likely it is to cause concavation for PP material injection molding.

Whereas the easier it is to produce shrinkage voids, such as PC material injection molding.

Therefore, after the injection molded part is prematurely released, it is appropriately cooled to maintain a certain hardness on the surface of the injection molded part so that it is not easy to cause surface sink marks.

However, if the problem of the sink is serious, the cooling will not eliminate the sink marks.

It is necessary to adopt a method of freezing water to make the surface of the molded part harden quickly to prevent shrinkage, but internal shrinkage holes will still exist.

For materials with a soft surface such as PP, due to vacuum and shrinkage force, the injection molded parts may have the possibility of a sink, but the degree of shrinkage has been greatly reduced.

At the same time, for the above measures, if the extended injection time is used instead of the prolonging cooling time, the surface sink and even the internal voids will be improved.

In solving the void problem, if the mold cavity temperature is too low, it will increase the degree of shrinkage. Therefore, the mold is preferably cooled by normal temperature water. Do not use frozen water.

If necessary, the mold temperature needs to be increased. For example, when molding PC material, the mold needs a higher temperature. When the temperature rises above 100 degrees, the improvement of the shrinkage voids will be good.

However, if it is to solve shrinkage concavation, the mold temperature can not be raised, but it needs to be reduced.
sometimes the above methods may not completely solve the sink problem. If surface sink marks must be completely solved, it is the last resort to have a proper amount of anti-shrinkage agent. Of course, transparent parts cannot use this way.